Custody and Visitation Issues: Poor Non-Custodial Living Conditions

My question involves a child custody case from the State of: Nebraska

My son has visitation arrangements with his son's mother. He also lives with his mother (my Ex). They live in a small house (he is in the basement) with several animals. At least 3 dogs and a cat, however I understand from someone else living in that household they have another 2 dogs that are usually kept in one of the bedrooms. (FYI- the extra 2 dogs puts them over the legal limit of dogs allowed in a residence per NE Humane Society)

The primary issue here is the house is not kept up well at all. (trying very hard to remain partial with my comments) The dogs have crated a habit of doing their business right inside the front door, which can go uncleaned for quite some time. It seems no attempt is being made at changing this habit which has been going on for quite some time (years).

Recently my grandson's mother was picking him up from the residence and had to walk through the excrement and urine from the dogs that have not been cleaned. Her son had to walk through it to get out of the house as well. She says this is the situation every time she picks him up from that residence. It is become routine now that the grandson has to have a bath and his clothes washed whenever he is picked up from the residence. (We also have had to wash him and his clothes whenever he comes from there to be with us)

Can the mother demand immediate cease on his visitation due to the conditions he is living in? If not, can she at least demand her child not be allowed to go over to that residence for his safety, even though that is where his father resides? Considering the non-custodial is my son, I am still in favor of the second option if possible. I am that concerned about my grandson being exposed to those conditions. I am also concerned for my son's health and have discussed this issue with him, however, unfortunately, he doesn't seem as concerned about it as I hoped he would be.